Corrosion resistant stainless type alloys



United States Patent 3,492,117 CORROSION RESISTANT STAINLESS TYPE ALLOYSRaymond P. Jackson, Suifern, N.Y., and Jacob Schramm,

Ringwood, and Daniel van Rooyen, Ramsey, N.J., as-

signors to The International Nickel Company, Inc., New

York, N.Y., a corporation of Delaware Filed Oct. 21, 1966, Ser. No.588,341 Int. Cl. C22c 39/20 US. Cl. 75-128 8 Claims ABSTRACT OF THEDISCLOSURE Alloys containing iron, nickel, chromium, molybdenum andcolumbium offer a high degree of resistance to stress corrosion crackingand intergranular attack. The molybdenum and columbium must becorrelated within certain ranges when the nickel content is 35% or more.

The present invention relates to corrosion resistant alloys of novelcomposition, particularly to improved alloys of the stainless typecapable of markedly inhibiting the onset of both stress-corrosioncracking and grain boundary sensitization while affording enhancedresistance to crevice corrosion and pitting in various chloride media.

Notwithstanding the many attributes and well established versatility ofthe austenitic stainless steels, one of the historically old drawbacksthereof has been their acknowledged propensity to undergostress-corrosion cracking, especially in respect of aggressive chloridecorrodents, e.g., boiling magnesium chloride. Numerous solutions to thismost difficult problem have been offered, two of the most recent andnotable being described in U.S. patents to Copson and Lang, Nos.3,159,479 and 3,159,480, wherein the background and nature of theproblem are also rather extensively treated. The proposals advancedtherein concern maintaining the elements phosphorus and nitrogen, interalia, at low levels in steels containing at least 19% nickel andchromium while utilizing a minimum amount of carbon or silicon (at least0.07% carbon, 1.7% silicon).

As so often is the case, however, the solution of one problem focusesattention on another. It is well known, for example, that high carbon(and this would include the minimum 0.07% referred to above) rendersaustenitic stainless steels quite susceptible to intergranularcorrosion, i.e., the steels are grain boundary sensitive. Intergranularcorrosion, which is particularly troublesome in connection withweldments, can, of course, be minimized in various ways. Ironically,perhaps, one of the most exemplary and accepted procedures is tomaintain the carbon content of such steels below about 0.03% as evidentfrom the now standard AISI 304L grade. Too, higher carbon contents canbe brought under control through stabilization with columbium, whenceevolved AISI 347. AISI 304L and 347 might circumvent intergranularcorrosion but in view of the Copson and 3,492,117 Patented Jan. 27, 1970"ice Lang development involving the use of at least 0.07% carbon,stress-corrosion cracking is accentuated. (High silicon as recommendedin the second patent above mentioned is discussed infra.)

Perhaps also noteworthy, both of the aforementioned patents admonishthat molybdenum should be kept at an extremely low order of magnitude,less than 0.075%; otherwise, stress-corrosion cracking is agravated. Butadherence thereto precludes obtaining the benefits conferred by the verymolybdenum contents (2% to 4%) largely responsible for the developmentof austenitic stainless steels AISI 316 and 317, steels which, however,are prone to stress-corrosion cracking, and intergranular corrosion athigh carbon levels. Data herein confirm that small amounts ofmolybdenum, say, up to 2%, are subversive, but for reasons presentlyunexplainable, molybdenum above about 3%, depending on alloy chemistry,begins to restrain rather than promote stresscorrosion attack andupwards of about 5.5% greatly inhibits cracking. This behavorial patternis illustrated infra. In any event, it would appear that a stainlesstype alloy was hitherto needed capable of effectively resisting bothstress-corrosion cracking and also intergranular corrosion and whichwould also offer appreciable resistance to crevice corrosion and pittingin chloride media.

It has now been discovered that with special alloys containingcontrolled amounts of iron, nickel, chromium, molybdenum, columbium,carbon, etc., the foregoing objectives can be accomplished.

It is an object of the invention to provide new corrosion resistantalloys.

Another object is to provide alloys of novel composition resistant tostress-corrosion cracking and intergranular corrosion attack while alsooffering outstanding resistance to crevice corrosion and pitting.

Other objects and advantages will become apparent from the followingdescription.

Generally speaking and in accordance with the present invention, alloyscontemplated herein contain (in percent by weight) at least 30% nickel,about 17% to 22% chromium, from about 5.5%, e.g., 6%, to 9.25%molybdenum, at least 1%, e.g., at least 1.5%, and up to about 3.25%columbium, up to 0.03% carbon, up to about 1.5% manganese, up to 1%silicon, up to 0.6% titanium, up to 0.6% aluminum, and the balanceessentially iron. While vanadium and copper can be present in thealloys, it is preferred that the amounts of these constituents notexceed 2%, respectively, since it has been found that they often detractfrom corrosion resistance. Elements such as oxygen, nitrogen,phosphorus, sulfur and the like should be kept at low levels consistentwith good commercial practice. In this regard, the respective amounts ofphosphorus and sulfur should not exceed about 0.02% and 0.03%.

In carrying the invention into practice, the alloys should contain atleast 30% nickel lest stress-corrosion cracking be promoted. It has beenfound that with alloys otherwise in accordance herewith, a range ofabout 31% to 34% nickel offers excellent resistance to stress-corrosioncracking even in the highly aggressive environment of boiling magnesiumchloride. Up to 40% nickel can be present, but in amounts above about35% and to consistently achieve highly satisfactory crevice corrosionresistance, it is quite advantageous that the nickel content becorrelated with the molybdenum and columbium as shown in Table I.

1y at least 25%, in obtaining the maximum by way of corrosionresistance.

In respect of other constituents, processing of the alloys isfacilitated with the presence of 0.1% to 0.5% of either aluminum ortitanium or both. Silicon above about 1% can bring about the occurrenceof weldability and workability difficulties and it is beneficial thatsilicon not exceed TABLE I Molybdenu1n+Co1um- Ni k 1 Molybdenum, percentColumbiurn, percent biurn, percent percent A B A B A B Column B denotesmost advantageous range.

Molybdenum should not fall below about 5.5%; other- 0.25%, it being ofadvantage to observe a maximum of Wise resistance to stress-corrosioncracking is endangered 0.1%. Manganese preferably does not exceed 1%.While, and, at best, crevice corrosion resistance is impaired. The asindicated above herein, up to 2% each of vanadium or data in Table II isof interest in illustrating that although copper can be present, amountsup to 1% and 0.75%, inconsequential amounts of molybdenum are an openinrespectively, are satisfactory. Tungsten, if present, should vitationto stress-corrosion cracking in magnesium c'hlonot exceed 1% andtantalum (if any) above 2% is not ride, the reverse is the case withmolybdenum levels uprecommended. Provided at least 1% columbium ispreswards of 5.5% or 6%. Usual testing procedures were emcut, it isconsidered that tantalum can be used in lieu of ployed, to wit, U-bendspecimens (annealed condition). columbium on an atom for atom basis, twoparts of tanwere immersed in boiling 42% magnesium chloride (154 talumfor one part of columbium. Finally, for purposes C.) and periodicallyinspected for a period up to days, of good deoxidation, it is mostfavorable that at least one the tests thereafter being discontinued. ofthe following elements be incorporated in the alloy TABLE II Ni, 0 c, s.41, T1, Cu, Days to percent percent percent percent percent percentpercent percent percent failure 41.8 18.3 0.07 n.a. 0.58 0.69 n.d. n.d.0.05 OK.

34.2 20.5 0.03 iii. 0. 71 0.83 0. 23 0.44 0.41 6.

5-2 a 922 3-22 at; 3-2 3-22 55.

n.d.=Not detected.

Balance of alloys iron and impurities.

In respect of the data in Table II, molybdenum-free, high melts; up to0.08% magnesium, up to 0.005% boron, up carbon Alloys A and B serve ascontrols. Reducing the to ()5% calcium nd up t 0,02% i o i Carboncontent y confirms the ease with wh In order to give those skilled inthe art a better undercrackillg Alloys D hrough G illustrate thedestanding of the invention, the following illustrative destructiveinfluence exerted by small amounts of moly scription and data are given:

denum, including high carbon Alloys D, E, and F (alloys Nickel, iron,chromium (vacuum grade), and carbon which otherwise would be expected tobe virtually crackwere charged into a magnesium oxide crucible. Uponfree Under A comparison of Alloys H and L melting under an argonblanket, columbium, molybdenum an M and N and P reflect that, geqefallySpeaklng, and manganese were then added, the melt being broughtmolybdenum above about 3% reverses 1ts role as a subto a temperature fabout 2900 R Upon cooling to Verslve- I 2850 F., aluminum, titanium and,excepting Alloy Q,

Qolumbmm Potentlany contrlbqtes to crevfce col-$1011 calcium-silicon ormagnesium was then added. The melts reslstanc? Rrovldedl d h g i g m i gOys were poured at about 2800 F. and cast into ingots which and that 1t18 cone ate t 6 me e an m0 y i were then hot rolled at about 2100 F. tospecimens A contents as set forth herein. Low amounts of columbmm, inchthick e.g., 0.2% or 0.5%, are not efiective and it is most ad- Secime'ns were then sub.ectd to at least one of two vantageous that atleast 1.5% be present in the alloys irkn t t th fi t J f M t respectiveof nickel content. Amounts above 3.25% are 2 kconsls mg m mg 0unnecessary and but serve to increase cost. To this might Stnp out 5 Inct (a cold f uctlon of about be added that cracking occurred when rollingan ingot at 1g thereafter z ji li 3 for 3 2100 F. concerning an alloycontaining 5% columbium, speclmens X 2 w mac W an the alloy otherwisebeing within the invention. Chromium "P Immersed for about 72 Pours 10%ferric ch10 below 17% adversely affects resistance to crevice corro-Tlde 801M191! rubber bands b61112 Wrappfid ihereafollnd t0 sion andamounts above 22% contribute to workability fOrIn cr The data Obtalfled011 a number of alloys problems. The alloys beneficially contain atleast 18% are given in Table III wherein in contrast to Alloys 1chromium with 21.5% being a preferred maximum. It is through Alloys Qthrough Y 4 Outside the inventionto be emphasized that the sum of thechromium plus Included are various commercrally produced prior art molbdenum Should be at least 24% most advanta eous- 5 allo s to wit Z andAA throu hDD.

TABLE III Ni, G M0, C Al, T1, Fe, Weight loss, percent percent percenpercent percent percent percent percent milligrams 30. 1 21. 8 6. 0. 0292. 2 07 Bal. 2. 5 32. 4 21. 6 6. 5 0. 021 2. 1 18 24 Bal. 0. 4 33. 5 21.2 6. 4 0.01 2. 1 25 Bal. 0. 1 35. 5 20. 0 6. 3 0. 025 2. 2 26 Bal. 1 0.75 35. 8 20. 2 7. 3 0. 031 3. 1 18 24 Bal. 0. 0 39. 7 19. 9 9. 1 0.0172. 2 25 21 Bal. 0. 7 36. 3 20. 3 0. 7 0. 023 0. 14 25 2. 45 Bal. 416. 539. 3 19. 8 6. 3 0.019 37 28 Bal. 208. 7 40. 0 20. 0 6. 25 0. 032 1. 1626 Bal. 101. 9 39. 0 22. 0 6. 15 0. 030 2. l8 24 Bal. 113. 4 38. 5 20. 06. 2 0. 054 2. 2 33 26 Bal. 154. 3 39. 0 20. 0 4. 35 0. 025 2. 1 22 24Bal. 176. 1 44. 2 19. 9 6. 15 0. 10 2. 1 32 25 Bal. 101. 2 43. 5 21. 66. 6 0. 038 2. 34 31 26 Bal. 88. 0 60. 8 20. 2 6. 0 0. 04 2. 1 30 27Bal. 97. 4

Other percent 45. 9 21.8 6. 56 0. 04 1. 96 0.32 W, 0.81 Co Bal. 16. 344. 5 21.5 6. 69 1. 13 Cu, 2.25 Ta, 1.06 1 Bal. 9. 2

43. 2 20.0 3. 03 1.75 Cu, 1.04 Ti 29. 9 544. 2 33.8 20. 1 2. 3 3.41 CuBal. 260 52. 5 19.0 3.0 5 2 0.1 Cu 18. 0 80. 6

Bal.=Balance plus impurities witn manganese not morethan about 1%. 1Average 012 s ecimens. 2 Contained 2.0 0 copper.

In respect of the data in Table III, Alloys Q through V 25 cal and otherfields, e.g., marine, petroleum, etc. The alare without the inventionprimarily by reason of the fact that the correlation of the percentagesof molybdenum and columbium and nickel content is quite inconsistentwith that set forth in Table I. Alloy 6 illustrates particularly well(compare with Alloy S, for example), that nickel between 35% and can besuccessfully employed provided the aforesaid relationship is observed.It will also be observed that the alloys within the invention comparedmore than favorably with the commercial alloys Z and AA through DD.

The second test involved the extremely severe boiling magnesium chloridetest referred to above herein. Test results are reported in Table IVregarding Alloys 1, 2, 3, 5 and 7 each of which is within the invention(Alloys 4 loys can be produced in various mill forms, including bar,rod, sheet, plate, strip, wire, etc.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. A stainless alloy resistant to both stress-corrosion cracking andintergranular corrosion and consisting essentially of from 30% to 40%nickel, about 17% to 22% and 6 were not exposed to the magnesiumchloride test). chromium, from 5.5% to 9.25% molybdenum, at least TAB LEIV Ni, Cr, M Cb, M Fe, Days to percent percent percent percent percentpercent percent failure 30. 1 21. 8 6. 5 0.029 2. 20 0. 70 Bal. 30

32. 4 21. 6 6. 5 0. 021 2. 10 0. 60 Bal. 30

33. 5 21. 2 6. 4 0.010 2. 10 0.70 Bal. 30

35. 8 20. 2 7. 3 0.031 3. 10 0.61 Bal. 30

35. 9 19. 7 6. 1 0. 020 2. 36 0. 70 Bal. 30

It will be observed that each of the alloys of Table IV resistedcracking for the full period of test. Alloys containing 35 to 40% nickelresist stress-corrosion cracking and also manifest excellent resistanceto crevice corrosion when the nickel is properly related to molybdenumand columbium in accordance herewith.

In the cold worked condition alloys in accordance herewith manifest highstrength. Alloy 6, for example, when cold reduced to a wire (a reductionof over 90%) was characterized by an ultimate tensile strength of about305,000 p.s.i. Equally important, the wire was sufiiciently ductile topass the kink test (a test wherein the wire is formed into a loop andthe ends are drawn together t tightly close the loop). Thus, aparticularly suitable use for such alloys would be for marine cableapplications.

Conventional processing procedures well known to those skilled in theart can be employed. Air melting practices as well as vacuum techniquesare quite suitable. Hot working operations can be carried out over atemperature range of about 1800 F. to 2300 F. and satisfactory annealingtemperatures are from about 1900 F. up to about 2150 F.

While alloys of the subject invention are useful in resisting thecorrosive effects of various chloride media in general, specificapplications include vessels, containers, tubing, piping, valves and thelike, employed in the chemi- 1% and up to 3.25% columbium, the nickel,molybdenum and columbium being correlated as follows when the nickelcontent is from 35% to 40% up to 0.03% carbon,

Molybdenum Molybdenum, Columbium, Oolumbium, Nickel, percent percentpercent percent Molybdenum Molybdenum, columbium, Columbium, N lckel,percent percent percent percent 4. A stainless alloy in accordance withclaim 2 containing 6% to 9% molybdenum.

5. A stainless alloy in accordance with claim 4 containing 1.5% to 3%columbium.

6. A stainless alloy in accordance with claim 5 containing 18% to 21.5%chromium and in which the sum of the chromium plus molybdenum is atleast 25%.

7. A stainless alloy in accordance with claim 1 containing 31% to 34%nickel, 18% to 21% chromium, 6% to 9% molybdenum and 1.5 to 3%columbium.

8. A stainless alloy in accordance with claim 1 and containing up to0.6% titanium, up to 0.6% aluminum, up to 2% of vanadium, up to 2%copper, up to 1% tungsten, up to 2% tantalum, up to 0.08% magnesium, upto 0.005% boron, up to 0.05% calcium and up to 0.02% zirconium.

References Cited UNITED STATES PATENTS HYLAND BIZOT, Primary ExaminerUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 9 ,17 Dated January 27, 1970 Inventor) RAYMOND P. JACKSON, JACOB 8c DANIELvan ROOYEN It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 8, for "agravated" read "aggravated". Column 3, line 59,for "potentially" read --potently--.

Column 6, line 52 (Claim 1, line 7), after "40%" insert a colon anddelete remainder of line.

Column 6, line 60 (Claim 1, line 1'4), before "up to 1.5% manganes'insert --up to 0.03% carbon,--.

5min Mb SEALED luv 17 m (SEAL) Atteet:

Emil-m1 m, r '4 r t a. AmtingCffiur oomissioner or M

